1. Field of the Invention
The present invention relates to a quartz-crystal controlled oscillator detecting an atmosphere temperature at which a quartz-crystal oscillator is placed, and controlling a heating unit based on a detection result of the temperature to keep the atmosphere temperature at a constant temperature.
2. Description of the Related Art
Normally, when a quartz-crystal controlled oscillator is incorporated in an application to which quite high frequency stability is required, an oven controlled crystal oscillator (OCXO) is generally used. Although temperature control in OCXO is structured by using discrete parts (e.g. an operational amplifier, resistance, and a capacitor) using a thermistor as a temperature sensor, it was not possible to perform temperature control over a range of ±20 m° C., for example, due to variation and aged deterioration of respective analog parts.
However, it is required that a quite high-stability clock signal should be used in a base station, a repeater station, etc. at a relatively low cost. For this reason, a situation to be difficult for the conventional OCXO to support is expected.
In FIG. 2 and FIG. 3 of Patent Document 1, it is described to structure two quartz-crystal oscillators (quartz-crystal resonators) by providing two pairs of electrodes on a common quartz-crystal piece. Further, paragraph 0018 describes that a frequency difference appears between the two quartz-crystal oscillators in accordance with a temperature change, and measuring of this frequency difference is equivalent to measuring of temperature. Further, a relation between this frequency difference Δf and an amount of frequency to be compensated is stored in a ROM, and an amount of frequency compensation is read based on Δf. However, this method is related to a temperature compensated crystal oscillator (TCXO) compensating an oscillation frequency based on a detected temperature, but is not related to the OCXO.
Further, as described in paragraph 0019, this method is required to adjust the quartz-crystal oscillators so that, regarding a desired output frequency f0 and respective frequencies f1, f2 of the two quartz-crystal oscillators, a relation of f0≈f1≈f2 is satisfied, and thus there are problems that a manufacturing process of the quartz-crystal oscillators becomes complicated, and besides, it is not possible to achieve high yield. Furthermore, clocks being frequency signals from the respective quartz-crystal oscillators are counted for a given period of time, and a difference between the clocks (f1−f2) is determined, so that a detection accuracy directly influences on a detection time, which makes it difficult to realize high-accuracy temperature compensation.
[Patent Document 1] Japanese Patent Application No. 2001-292030